The present invention relates to additives or conditioners for oil well drilling fluids, and more particularly to a boron-chrome lignosulfonate drilling fluid additive or conditioner.
The most commonly used drilling fluids are aqueous dispersions of clay. The drilling fluid or "mud" is pumped down a hollow drill string, through the bit at the bottom, and up the annulus formed by the hole or casing and the drill string to the surface. After reaching the surface, various operations are performed on the drilling fluid to remove the cuttings and formation material thereform. The drilling fluid is then treated with additives to obtain a desired set of rheological properties, and is then pumped back into the well in a continuous circulating process.
A satisfactory drilling fluid must have various desired functions, such as gelling during temporary work stoppage and other functions well known in the art, which contribute to the success of the well drilling operation. In order to accomplish these various functions, it has been found necessary to incorporate certain additives in the drilling fluid. Modified lignosulfonates derived from spent sulfite liquor obtained from the pulping of woods have proven to be effective additives for obtaining the desired properties in drilling fluids.
In order to improve the effectiveness of the liqnosulfonates as drilling fluid additives, King et al. U.S. Pat. No. 2,953,473 recommended the use of certain metal salts of liqnosulfonate wherein the metals are chromium, aluminum, iron, copper or combinations thereof, which salts may or may not be oxidized. Of the metal lignosulfonate salts disclosed in the King et al. patent, the chromium salt has been found to be very effective so that the chromium salt by itself or in combination with other metals has become commonly used as a drilling fluid additive. See for example, Hoyt, U.S. Pat. No. 3,035,042 in which the additive is an iron-chromium lignosulfonate complex, and Van Dyke et al. U.S. Pat. No. 3,076,758 wherein the additive is an iron-free chromium lignosulfonate. Chrome-free additives are also well known, and Kelley U.S. Pat. No. 4,374,738 is an example of such a drilling fluid composition. Additionally, boron has been complexed with chrome free lignosulfonates for drilling fluid additives as discussed in application Ser. No. 06/372,141 filed Apr. 27, 1982, now U.S. Pat. No. 4,457,853, and assigned to the assignee of the present application. Boron has also been added to lignosulfonates to increase set times for oil well cementing compositions as described in Childs et al., U.S. Pat. No. 4,149,900.
One problem with utilizing lignin containing products such as the spent sulfite liquor from pulping processes to produce a chrome complexed drilling fluid additive is that such liquor does not contain pure lignosulfonate. The spent sulfite liquor generally contains only about 40% to 60% by weight lignosulfonates with the remainder being carbohydrates and other organic and inorganic constituents dissolved in the liquor. If these carbohydrates remain in the liquor, they react with chrome during the oxidation-reduction-complexing reaction to form a gel resulting in a poor quality oil drilling mud conditioner. As a result, the spent sulfite liquor must be subjected to different treatments such as alkaline, acid, or heat treatments as well as reacted with other chemicals to modify or remove various undesired non-lignin constituents. However, such additional processing of the spent sulfite liquor is costly. It is thus desirable to provide a high quality chrome lignosulfonate for use as an oil well drilling mud conditioner which is produced from less pure spent sulfite liquors containing sugar acids and polysaccharide carbohydrates.